Kamal al-Din al-Farisi

Kamal al-Din Abu al-Hasan Muhammad ibn al-Hasan al-Farisi was born in 1267 CE in Tabriz, in the Persian region of what is now northwestern Iran. His family background placed him within an educated, scholarly milieu that nurtured his intellectual curiosity from an early age. He studied under the great polymath Qutb al-Din al-Shirazi, himself a student of Nasir al-Din al-Tusi, placing al-Farisi within a distinguished chain of scientific transmission.

Al-Farisi's most celebrated achievement was his rigorous mathematical explanation of the rainbow, set forth in his landmark work Tanqih al-Manazir (Revision of the Optics). Building upon Ibn al-Haytham's foundational Kitab al-Manazir, al-Farisi conducted meticulous experimental investigations using glass spheres filled with water to simulate raindrops. He correctly demonstrated that rainbows result from two refractions and one internal reflection of sunlight within individual water droplets, and he provided a geometric account of both the primary and secondary rainbows. This explanation predated Descartes' independent derivation by more than three centuries.

Beyond the rainbow, al-Farisi made significant contributions to the theory of light and color, the mathematics of perspective, and number theory. His work on amicable numbers — pairs of integers where each equals the sum of the proper divisors of the other — was particularly notable.

Al-Farisi spent most of his scholarly life in Tabriz, which under the Ilkhanid dynasty had become a vibrant center of learning. He died there in 1319 CE, leaving behind a body of work that would influence later generations of opticians and mathematicians in both the Islamic world and, eventually, Renaissance Europe. His patient experimental methodology stands as a model of empirical rigor.